THE BLACK ART

TRANSMISSION REBUILDS EXPLAINED

Gearboxes — they make sense and most blokes can get their heads around how they work. Power goes in one side and out the other, and, in the middle somewhere, different-sized gears interact to alter the output speed. Automatic transmissions, however — those are a whole different story; perhaps it’s the confusing part about fluid transferring power rather than a mechanical connection. Whether we are talking about a transmission you’ve seen at a swap meet or one that’s in a vehicle you are lusting after, buying an automatic gearbox without a warranty or proof of what and when reconditioning work has been done to it can be a minefield. Add to this the fact that most automatic V8 vehicles will be fitted with slushboxes that will have seen decades of service under God only knows what kind of driving and service conditions, and the uncertainty increases. If all that doesn’t sound bad enough, hold tight for the really good news: just because a transmission seems to work OK during a quick test drive, there’s no guarantee that it won’t give you big trouble a few kilometres down the road — more than likely, just after you’ve handed over that wad of hard-earned cash for your new ‘dream’ ride or swap-meet trans. All that being said, the transmissions fitted to the vast majority of vehicles we drive are incredibly reliable engineering masterpieces that will give many years of trouble-free operation in any number of applications. The other good news is that, depending on your application and requirements, almost anything can be repaired. If you know what to look for and how to approach solving problems when they arise, you will be in a much better place. We spoke to Michael Clarke from Kaspa Transmissions in Glenfield, Auckland, to get a better understanding. When buying a transmission, it’s all about reducing the factors that add up to the likelihood of trouble. If the transmission is in an operational vehicle and it functions well during a test drive, the car is very low mileage, and the vehicle has been well maintained and cared for overall, the odds of the transmission being trouble-free increase. Similarly, if you have receipts or a warranty for work done, and can verify when it was done in relation to kilometres travelled, things are looking better. When test driving an automatic trans, make sure there is no delay when shifting into drive and reverse. Drive it through the gears gently at first and then harder. Check for unusual slipping or lag between gears, and listen out for clunks. Old transmissions may have some whine or clunk but unusually loud noises mean problems. Also, be sure to check fluid level and quality.

DRIVE THROUGH THE GEARS, GENTLY AT FIRST AND THEN HARDER

In the absence of receipts for work done and points of reference as to the condition of the trans, the most important things you can verify are whether the transmission is the vehicle’s original unit, how many kilometres the trans has done, and the service history. If it’s not the original unit, you need to ask for receipts for any work done — otherwise there is no way the seller can prove to you the condition of the transmission. No receipts for work done means you really have no idea what’s going on — it’s a gamble. Michael told us that he’d be a rich man if he had a dollar for every time someone has brought in a vehicle, having been told, “The trans has been rebuilt” by the person they bought it off, only to find it’s worn out. Get proof or take a risk. If the trans is not in a vehicle, and you don’t have receipts, it’s a total gamble. When it comes to classic cars, the staple transmissions are the GM Powerglide, Turbo Hydramatic 350s and 400s, Ford C4s and C6s, and the Chrysler TorqueFlite. In recent years, Michael has seen more people opting to recondition the older transmissions — such as the Hydramatics — rather than trashing them, to keep their vehicles original.

WHEN TRANSMISSIONS ARE TAKEN APART, IT IS RARE TO FIND CATASTROPHIC DESTRUCTION

More upgrades and options these days make rebuilding easier than ever, and you can end up with a better and stronger trans. You are no longer stuck with three speeds, either — it’s possible to add gears to transmissions. It’s for this reason that Michael doesn’t really encourage buying the external overdrive units that are available. They work, but often you can modify your existing transmission or get a whole new unit more cheaply than you can buy bolt-on overdrives and the adaptors required to make them fit with your drivetrain. Michael informed us that when transmissions are taken apart, it is rare to find catastrophic destruction — these are well-made machines with tight tolerances and parts that are bathed in oil and sealed in a case. What happens is that, over time, parts wear out. This is especially true of classic transmissions, in comparison with late-model stuff that may be junk once it’s worn out. Unlike so much of the stuff we use in daily life, old stuff was made to last and made to be repaired, not chucked out after its projected service life. Once stripped down and cleaned, transmissions usually simply require the installation of overhaul kits that include seals, gaskets, teflons, frictions, steels (clutch packs), and the band. Often, depending on the application, shift kits will also be installed to change the feel and point at which the transmission shifts gears. For performance applications, valve bodies may also be changed to allow for full manual operation.

The other thing that needs to be checked is the torque converter. To access the inside of this, the converter shell is cut open and the condition and pitch of the fan blades inside are checked and, if necessary, fixed. The pitch of the blades will affect the operation of the transmission — you may have heard people talk about a converter’s ‘stall’; this is determined by the angle and pitch of the blades in the converter and the effect of that on the trans fluid. When discussing a job with a customer, Michael first establishes the application and the use for the transmission. This means understanding the type of vehicle it’s going in — size and weight — what the horsepower and torque levels will be; and, most important, what the customer is going to do with it. Repairs and modifications are always done to a high spec, but some applications — such as the serious power of drag racing — require stronger parts for higher performance. Michael said that looking after your transmission once it’s been rebuilt will make it last much longer. He stressed that you must not underestimate how important it is to keep the quality of the fluid good by regularly changing it and making sure the level is correct. If your vehicle is fitted with an external trans cooler, make sure it’s up to the job. Changing the filter and ensuring kick-down cables and vacuum pressures are adjusted correctly are also vital elements in preventing transmissions slipping or burning up. So, there you go. Whether you are looking to maintain originality in a rare vehicle, improve performance for a race or heavy-duty service application, improve usability by adding gears, unsure about the condition of a used transmission, or just plain wanting to get that project rolling again, there are many options and the process need not be confusing or a financial minefield. The venerable auto trans need not be a mystery; rather, it should be seen as what it is: a clever work of mechanical art that can be fashioned to perform exactly as you desire.